I have an Eee PC 701 4G, and some time ago I disabled its wireless NIC in the BIOS to save energy. Now I've come to need it working again, but I can't re-enable it, because it always goes back to being disabled after I boot the eeebuntu installed on the machine. If I just enable it in the BIOS, reboot and go into the BIOS setup again, it's still enabled, but if I let the OS load it'll get disabled. I'm really at a loss here, how do I find out what's wrong? Could it be Ubuntu that does this?

I would double check that you are saving the settings when you are exiting the BIOS.

Next, are you using Windows and did you install it yourself? If you disabled the wireless before installation, it is possible that Windows simply does not have the wireless drivers. I would recommend that you perform an update and try the physical/soft switch (I do not know on your laptop) to enable the Wireless.

(On my laptop, the BIOS reports the last used setting, so in Windows, if I use a hotkey FN+F1 to disable, it will show disabled in BIOS)

If you do not have success in any of these, I would suggest that you perform a BIOS update as this should also reset any settings in the process.

If you are running one the Linux variants and it has any sort of power management applications running check to make sure the wireless nic isn't disabled in there. I know on mine there is the eee-control applet which allows me to disable the nic and card reader.